Sit-up exerciser



FIG. 1 is a perspective view of a sit-up exerciser, showing my new design;

FIG. 2 is a front elevational view thereof, the rear being a mirror image of the front shown in FIG. 2;

FIG. 3 is a left side elevational view thereof;

FIG. 4 is a right side elevational view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom view thereof. 

The ornamental design for a sit-up exerciser, as shown and described. 